My question is this. Does a parked vCPU core still need to be scheduled on the Host CPU?
I have Googled around a bit and I have certainly found quite a few differing opinions on whether or not it is better to disable core parking or leave it enabled, but I haven’t found an answer to this basic question.
I recently noticed on one of our Server 2012 VMs with several of its cores parked. The processor usage on this VM is variable. There are often times when the machine is not heavily used but when it is needed, it needs to be able to respond quickly and it needs all of its cores to do so. At times processor usage can go back and forth between 2% and over 90% quickly. During these time I notice the vCPUs parking and un-parking quite a bit and I know that, kind of activity can have an adverse effect on performance.
My first though was to simply shut off core parking in Windows to avoid performance problems at these times, especially since there is no power saving benefit for the VM, but then it occurred to me that if a parked core doesn’t need any resources from the Host machine leaving parking on could help with CPU contention on the host when the VM is idle. If, on the other hand, a parked vCPU still needs to be scheduled on the host CPU then there would be no advantage to leaving parking enabled and I should just set the power scheme on the VM to “High Performance” to shut off core parking.
So, does anyone know whether or not a vCPU core on a guest VM that is in a parked state still needs to have idle cycles scheduled on the host CPU?